This study of the respiratory health effects of direct human exposures to acidic substances in ambient air will employ complementary observational epidemiologic methods in two phases. The initial phase of this research will involve a longitudinal observational epidemiologic study in New York State which will utilize the N.Y. Statewide Planning and Research Cooperative System (SPARCS) hospital admissions data in conjunction with daily direct acid aerosol measurements which we propose to make in five urban communities expected to have varying acid exposures. The health effects assessment will include linear regression and time series analyses of these data to discern statistical associations between acute exposures to ambient acid aerosols and daily hospital admissions for respiratory disease. The second phase of this research will seek to discern chronic respiratory health effects via a detailed prospective epidemiologic field study comparing two cohorts of 50 schoolchildren in Phase I communities with (then documented) significantly different acid aerosol concentrations. This work will include the use of questionnaires, personal activity journals, and indoor sampling to assess individual acid aerosol exposures. Objective lung function measurements and symptom records will be made daily for each participant over a campaign period of two weeks and at least two campaigns will be conducted in each community so that acute effects, which might otherwise confound cross-sectional comparisons based upon single measurements alone, may be controlled for in the data analysis. Moreover, the additional use of the Aerosol Dispersion Technique (ADT) recently developed will provide greater sensitivity in the detection of potential lung function effects of exposures at ambient acid aerosol concentrations. The Phase II health effects analysis will include the use of linear regression models on individuals and repeated measures ANOVA on the collective observations. Together, the Phase I and Phase II analyses will provide a balanced investigation of the potential for acute and/or chronic respiratory health effects to occur in the general public from acidic aerosol exposures typical of those experienced in the Northeastern U.S.